1. Field of the Invention
This invention relates to a friction material and method for controlling fluid flow, and, more particularly, to a facing material having a plurality of channels of varying dimensions as described herein.
2. Description of Prior Art
In clutches, brakes, manual or automatic transmissions, limited slip differentials, hoists and similar friction power transmissions and energy absorption devices, there is generally provided one or more sets of cooperating members in which one of the cooperating members drives the other. It is not uncommon for these cooperating members to move in a cooling medium or liquid, which is generally some type of lubricating oil, and frequently the oil is forced to circulate about and between the engaging surfaces of the cooperating member so as to continuously lubricate and cool them. In order to accomplish circulation of the cooling medium within blocker rings, clutch plates, transmission bands and the like, the prior art has provided grooves or slots directly in the engaging surfaces of one or both of the cooperating members or in friction materials fixed thereto. For example, various materials and devices may have a brass coating or a paper lining as seen in U.S. Pat. Nos. 4,267,912; 4,878,282; 4,260,047; 6,065,579; and 5,615,758, all of which are incorporated herein by reference and made a part hereof.
In the past, forming grooves within the friction materials of cooperating members typically added complexity to the manufacturing of such friction material and the power transmission-absorption device.
In order to facilitate or eliminate the hydrodynamic friction stemming from oil or cooling medium lying on the surface of the friction material engaging the driving member, an improved friction material for circulating the cooling medium is preferred.
Prior art friction materials also include certain pyrolytic carbon friction materials as seen in U.S. Pat. No. 4,700,823 to Winkler and U.S. Pat. No. 4,291,794 to Bower. In such friction material, a meshed cloth substrate formed of carbon fibers is provided with a coating of carbon or other material being deposited on the fibers by chemical vapor deposition. This type of friction material has a characteristic of a relatively open mesh, which allows ready penetration by an adhesive for improving bonding as well as a certain degree of veracity therethrough. However, as pointed out in U.S. Pat. No. 4,291,794, grooving material of such material is still provided in order to permit the flow of the cooling fluid between the friction faces of the cooperating members of the power transmission or energy absorption assembly. This type of friction material also does not easily provide highly bonded fibers as friction surface of the material nor does it achieve a highly controlled texture as needed when it is desired to control fluid flow. Moreover, it has been found that such friction material is difficult to compress to a desired thickness, such as during the process of bonding it to a member.
U.S. Pat. No. 4,878,282 illustrates a method for producing friction plate, synchronizer blocking rings and similar structures which use friction lining material applied as a continuous member on a support where the ends of the grooves are open by removal of the friction lining material which close the grooves. This requires several manufacturing steps, including cutting the material, assembling the material to the support, densifying the material once it was on the support and the trimming of a portion of the material. Unfortunately, the use of this type of process created, for example, about 20% scrap material.
U.S. Pat. No. 6,065,579 provided an improved system and method over the prior art. In that reference, a material for an element of a power transmission-absorption assembly and the method of making such material is disclosed. The material had a pre-selected channel configuration to discourage the formation of hydrodynamic oil films that create poor cold shift characteristics and to create a path for trapped oil at the friction interface. Another embodiment of that invention disclosed a material and method for slotting the material and situating the material on a blocker ring to facilitate providing a plurality of space grooves having an open end which was substantially larger than the closed end. The material optionally included a raised rib or chamfer which facilitated controlling the fluid at an area of engagement between the material and a mating friction member. FIGS. 18–21c of the reference illustrate a friction material referred to in the reference, showing a plurality of slots.
What is needed, therefore, is an improvement over the prior art which provides means, material and process which further facilitates providing a desired amount of fluid flow across the friction-facing environment and which, for example, further facilitates controlling, increasing and/or decreasing fluid flow across a surface of the facing material.